Dylan  Iqbal

Dylan Iqbal


4 Uses of JavaScript's Array.map() You Should Know

Array.map() is a very powerful method in JavaScript. In this post, we’ll look at 4 noteworthy uses of the .map() in JavaScript.

From the classic forloop to the forEach() method, various techniques and methods used to iterate through datasets abound JavaScript. However, one of the more popular methods is the .map() method.

.map() creates an array from calling a specific function on each item in the parent array. .map() is a non-mutating method in that it creates a new array as against mutating methods which only make changes to the calling array. This can be tricky to remember.

In this post, we’ll look at 4 noteworthy uses of the .map() in JavaScript. Let’s begin!

Table of Contents

Calling a Function on Each Item in an Array

.map() as earlier stated accepts a callback function as one of its arguments and an important parameter of that function is the current value of the item being processed by the function. This is a required parameter. With this parameter, we can modify each individual item in an array and create a new function off it. Here’s an example:

const sweetArray = [2, 3, 4, 5, 35]
const sweeterArray = sweetArray.map(sweetItem => {
    return sweetItem * 2

console.log(sweeterArray) // [4, 6, 8, 10, 70]

This can even be simplified further to make it cleaner with:

// create a function to use
const makeSweeter = sweetItem => sweetItem * 2;

// we have an array
const sweetArray = [2, 3, 4, 5, 35];

// call the function we made. more readable
const sweeterArray = sweetArray.map(makeSweeter);

console.log(sweeterArray); // [4, 6, 8, 10, 70]

Having code like sweetArray.map(makeSweeter) makes that a bit more readable when you jump into this code.

Converting a String to an Array

.map() is known to belong to the Array prototype. How about we use it to convert a String to an Array. Not to worry, we are not developing the method again to work for strings rather we will use the special .call() method.

Everything in JavaScript is an object and methods are just functions attached to these objects. .call() allows us to utilize the context of one object on another. Therefore, we would be copying the context of .map() in an array over to a string.

.call() can be passed arguments of, the context to be used, and “parameters for the arguments of the original function”. Sounds like gibberish? Here’s an example.

const name = "Chuloo"
const map = Array.prototype.map

const newName = map.call(name, eachLetter => {
    return `${eachLetter}a`

console.log(newName) // ["Ca", "ha", "ua", "la", "oa", "oa"]

Here, we simply used the context of .map() on a String and passed an argument of the function which .map() expects. Voila! We have a wolf-lang looking characters in our console. Yikes!

This functions like the .split() method of a String only that each individual string characters can be modified before being returned in an array.

Rendering Lists in JavaScript Libraries

JavaScript libraries like React utilize .map() to render items in a list. This requires JSX syntax however as .map() method is wrapped in mustache-like JSX syntax. Here’s a good example of a React component.

import React from "react";
import ReactDOM from "react-dom";

const names = ["john", "sean", "mike", "jean", "chris"];

const NamesList = () => (
    <ul>{names.map(name => <li key={name}> {name} </li>)}</ul>

const rootElement = document.getElementById("root");
ReactDOM.render(<NamesList />, rootElement);

Are you unfamiliar with React? This is a simple stateless component in React which renders a div with a list. The individual list items are rendered using .map() to iterate over the names array initially created. This component is rendered using ReactDOM on the DOM element with id of root.

Reformatting Array Objects

How about handling objects in an array? .map() can be used to iterate through objects in an array and in a similar fashion to traditional arrays, *_modify the content of each individual object *_and return a new array. This modification is done based on what is returned in the callback function. Here’s an example:

const myUsers = [
    { name: 'chuloo', likes: 'grilled chicken' },
    { name: 'chris', likes: 'cold beer' },
    { name: 'sam', likes: 'fish biscuits' }

const usersByFood = myUsers.map(item => {
    const container = {};

    container[item.name] = item.likes;
    container.age = item.name.length * 10;

    return container;

// [{chuloo: "grilled chicken", age: 60}, {chris: "cold beer", age: 50}, {sam: "fish biscuits", age: 30}]

All we did is simply modify each object in the array using the bracket and dot notation. This use case can be employed to process or condense received data before being saved or parsed on a frontend application.


In this post, we looked at for main uses of the .map() method in JavaScript. A thing to note is that in combination with other methods, the functionality of .map() can be extended and utilized powerfully. Try to find out more use cases. Leave your comments, questions, and feedback in the comments section, they’ll be appreciated!

#javascript #web-development

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4 Uses of JavaScript's Array.map() You Should Know

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Lowa Alice

Lowa Alice


JavaScript Arrays Tutorial. DO NOT MISS!!!

Learn JavaScript Arrays

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The origin of the article: https://www.youtube.com/watch?v=oigfaZ5ApsM&list=PLTjRvDozrdlxEIuOBZkMAK5uiqp8rHUax&index=4
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Thanks for visiting and watching! Please don’t forget to leave a like, comment and share!

#arrays #javascript #javascript arrays #javascript arrays tutorial

Giles  Goodwin

Giles Goodwin


Maps in JavaScript

What topics we are going to cover?

  1. What are Maps?
  2. What are the methods used in it and how we can insert or retrieve values to it?
  3. How Maps works, behave with loops and what is happening behind the scenes?

What are Maps?

By the word Map, here I mean another new method which is being used these days in modern JavaScript. Here we are going to see the classic dataType of Map. Mostly Map is getting used in looping concepts that’s a great thing, but if you go directly for all those then you won’t be able to understand the classic dataType of Map.

So let’s fire up our code editor and understand the concepts of Map with some amazing examples.

var myMap = new Map();

This is almost kind of constructional approach, where we create an object from prototype and stuff like that.

What are the methods used in Maps?

Now Map has a lot of properties and I think you should take a look at it, at once. So whenever you gonna type myMap. then you can see a list of methods will be appearing on your screen like- get, set, forEach, values, and bunch of things. So one of the common methods which are being used widely is set and get method and by this time I guess from its name itself you might have guessed it like these are some default setters and getters means it can add values to them and retrieve values from them.

How to insert values in Maps?

Let’s go ahead and try with set() method and have some of the fun together:

Note: They work almost like objects but remember this, Maps are not like objects, they are completely different.

var myMap = new Map();
myMap.set(1, "Ricky"); //myMap.set(any key, any value)
myMap.set(2, "Monty"); //myMap.set(any key, any value)
myMap.set(3, "Henna"); //myMap.set(any key, any value)
myMap.set(4, "Monta"); //myMap.set(any key, any value)

Now if you try to run this code in your editor, then you gonna see an output like this on your screen.

Map(4) { 1 => 'Ricky', 2 => 'Monty', 3 => 'Henna', 4 => 'Monta' }

Notice here, how Maps by default itself is telling you that how many properties you are storing in it and one more thing you can see here they have used => these arrow between its key, value pair to differentiate, and make you understand that they are not your regular objects.

#javascript-development #maps #array-methods #arrays #javascript

Coy  Roberts

Coy Roberts


Definitive Guide to Understand Javascript Array reduce()

Javascript array reduce() is an inbuilt method that is used to apply a function to each element in the array to reduce the array to a single value. The reduce() function executes the provided function for each value of an array from left-to-right. The return value of a function is stored in an accumulator.

Understanding Javascript array reduce()

JavaScript array reduce() is one of the pioneer function of functional programming. The reduce() method accepts two parameters, the total and the current value. If you want to add all the values of an array, then use the array reduce() function.

It is similar to both  Javascript map() and  Javascript filter() but, it differs in the callback arguments.

The callback now receives an accumulator (it accumulates all the return values. Its value is the accumulation of a previously returned accumulations), a current value, a current index, and finally, the whole array.

#javascript #javascript map #javascript filter #javascript array reduce

Terry  Tremblay

Terry Tremblay


Fill and Filter in Array in JavaScript

By the word Array methods, I mean the inbuilt array functions, which might be helpful for us in so many ways. So why not just explore and make use of them, to boost our productivity.

Let’s see them together one by one with some amazing examples.


The _fill()_ method changes all elements in an array to a static value, from a start index (default _0_) to an end index (default _array.length_). It returns the modified array.

In simple words, it’s gonna fill the elements of the array with whatever sets of params, you pass in it. Mostly we pass three params, each param stands with some meaning. The first param value: what value you want to fill, second value: start range of index(inclusive), and third value: end range of index(exclusive). Imagine you are going to apply this method on some date, so that how its gonna look like eg: array.fill(‘Some date’, start date, end date).

NOTE: Start range is inclusive and end range is exclusive.

Let’s understand this in the below example-

//declare array
var testArray = [2,4,6,8,10,12,14];


When you run this code, you gonna see all the elements of testArray will be replaced by 'A' like [“A”,"A","A","A","A","A","A"].

#javascript-tips #array-methods #javascript-development #javascript #arrays